Sand bunkers, also called sand traps, are sandy depressions which are interspersed along a golf course, typically in vicinity of the putting green and hole. They are intended to impede the motion of a golf ball which flies or rolls into them, but at the same time to enable a golfer to hit such a ball while it lies on the surface. Sand bunkers are located according to the design of the golf course architect. Their placement and configuration is in part limited by the geography of the other natural and man made features of the course. While sand bunkers are configured and placed to present a challenge to the golfer, they also have an esthetic aspect—presenting a pleasing appearance, by themselves and as part of the whole of the golf course.
Since sand bunkers are often placed on slopes, and often themselves have slopes, there is a tendency over time for the sand to move to about in the bunker under influence of such as wind, gravity, rain and golfers. Also, the sand can become contaminated with soil and debris. Thus, bunkers must be maintained by the golf course personnel for functionality and appearance. Often times, this means running rakes across the surface to redistribute and smooth the sand and to remove debris.
It is desirable that a golf course as a whole, and any bunker in particular, present consistent difficulty to players over time and under varying weather. That aim is defeated if water accumulates in the sand of the bunker because the character of the sand is changed by excessive wetness. Thus, when bunkers do not have self-draining shapes, or are situated on soils which do not have good permeability to water, then a drainage system is often installed.
In familiar types of bunker drainage systems, there is a trench within the soil beneath the depression into which bunker sand is placed. Usually a perforated conduit or pipe runs through stone or coarse gravel which fills the trench, to a discharge point away from the bunker.
Sometimes the sand of the bunker fills the trench and surrounds the pipe. Other times, the trench contains sand. A filter fabric called geotextile is usually placed on top of the gravel or stone, to prevent sand from entering and clogging the gravel or stone. Likewise, if a perforated pipe is surrounded by sand, the pipe is circumscribed with geotextile, to prevent sand from entering the openings in the pipe. In another variation, a perforated pipe is circumscribed by a layer of closed cell plastic foam pellets, which layer in turn is circumscribed in part or whole by geotextile and by granular media within the trench.
One of the problems with any system that uses geotextile is that the fabric can be snagged and torn by manual or powered rakes which are used for bunker maintenance, and the system will then fail in its intended function. Drainage systems which comprise pipes having relatively small openings are prone to filter fabric clogging when it is attempted to keep fine particles from entering the drains. On the other hand, if a coarse geotextile is used, then too much sand can flow into the drain, the piping can become clogged or the bunker depleted.
In some situations, it is an aim to store the water which flows into the drain beneath the surface of the earth, so it can either then dissipate it into the soil over time or be pumped out over time. However, providing sufficient size of underground reservoirs can be costly. And it can be a problem if the capacity of the reservoir is exceeded, if the drain then fails to function.
While the prior art systems are effective for their intended purpose in many instances, improvements are always sought in terms of drainage system cost (including transport and installation), durability and lowered maintenance.